It is known that data may be inputted to data processing devices by the use of keyboards having a plurality of input keys, with each key corresponding to a particular data element such as an alphanumeric character. A typical configuration of such a keyboard is known as a "QWERTY" configuration, wherein the first keys on one of the keyboard rows respectively represent the alphabetic characters Q, W, E, R, T and Y. However, such keyboards require a large number of keys and associated switches, and thus require a large amount of space, interfering with true portability and simplicity of construction.
Data input devices are also well-known which sense the position of a stylus contacting the face of a display device which permit the input of data to a data processing device without a keyboard. The touching and actual path of the stylus across the face of the display device is interpreted by a processor associated with the display device to provide data entry which permits a user to handwrite or select displayed data inputs. One form of these devices is known as a personal digital assistant (PDA).
U.S. Pat. No. 4,381,502 discloses the encoding of alphanumeric characters by a sequential depressing of keys in which a first key is not released until a second key is depressed. The encoding of letters is produced by depressing the key which is marked with the letter to be encoded as the second key in the sequence. This process is disadvantageous because it requires each of the keys to depict numerous letters or characters which makes use of the keyboard potentially confusing and complex. Furthermore, the order of input of the keystrokes determines the character which is selected (i.e. a 0-1 sequence inputs a different character than a 1-0 sequence which makes the input sequence susceptible to operator error).
U.S. Pat. No. 4,042,777 discloses a keyboard which generates specific characters by the combined selection of several keys.
U.S. Pat. No. 5,493,658 discloses a keyboard which is marketed as a BAT keyboard by Infogrip Inc. of Ventura, Calif. The keyboard of the '658 Patent utilizes a five key configuration intended for use by the blind. This keyboard utilizes the combined selection of keys to input information.